CMOS image sensor chips are typically used in mobile devices such as cell phone cameras to capture images (e.g. cell phone camera or video functionality). These image sensors are usually very small and compact, given the limited size and weight requirements for mobile devices. The image sensor chip includes one or more lenses that are used to focus the incoming light onto a light sensor. The light sensor converts the incoming light into electronic signals that represent the image formed by the incoming light.
Lenses are often made of glass or polymer, and are typically made using a molding process. For example, polymer lenses are typically manufactured using molding techniques such as stamping, injection molding and transfer molding. Injection molding, for example, involves injecting polymer in a liquid state into a mold cavity. The polymer is then cooled so that it solidifies in the shape of the mold. The polymer is then removed from the mold in the form of a lens.
Molded lenses are easily mass-produced. For example, pluralities of molds are simultaneously injected with fluid state material, then cooled, resulting in simultaneous formations of lenses. The quality of lenses needs to be high and consistent. However, as lenses get smaller and smaller, it has become harder to maintain quality with molded lenses because of the difficulty in forming multiple molds with exactly the same dimensions. Additionally, molds can fatigue over time and thus can produce lenses with declining quality over time. Lastly, injection molded lenses are monolithic, meaning that the possible optical properties achieved from molded lenses are limited. Multiple monolithic lenses can be stacked to achieve more varies optical properties, but with incrementally larger overall sizes and cost.
There is a need for an improved lens and manufacturing technique for making the lens that provides superior quality, uniformity and diverse optical performance over molded lenses, without adding significant cost.